1. Technical Field
The present invention relates to the testing of liquid samples. More specifically, the invention relates to a method for combining liquids for testing a liquid sample, the sample to be tested being combined quantitatively with a liquid medium. In addition, the invention relates to a test unit utilizing said method, and to a system including a plurality of such test units.
2. Discussion of Related Art
The invention is mainly implemented in the field of clinical chemistry, i.e. in analyses of medical specimens from patients for diagnostic purposes. A second central field of application relates to the analyses of samples from industrial processes, waste treatment and the environment.
Chemical tests are nowadays conducted in laboratories by means of analyzers, which are mechanized high-speed dispensing robots, whose operation is based on the transfer of liquids between open vessels. Such analyzers draw the samples to be tested and the reagents required for the tests from open tubes or containers into pipettes, transfer them by pipette suction into measuring filter troughs, perform mixing, and after the reaction, determine a parameter yielding the measurement result. The analyzer operation is controlled by measurements performed accordingly on reference samples with known contents.
Current analyzers have the benefit of high capacity, large test range and easy test variation. On the other hand, they have shortcomings relating especially to the open sample and reagent vessels and filter troughs and to the liquids being transferred by pipette suction between the vessels. Open vessels impair the conservation of liquids and expose the liquids to microbiological or similar contaminations. At the pipette suction stage, small air bubbles tend to be drawn alongside with the liquids, the air bubbles causing a corresponding volume error in a liquid batch that has been quantitatively dosed. At the injecting stage, again, a liquid droplet may occasionally remain at the pipette end under the effect of surface tension and thus be excluded from the analysis and result in a dosage error.
In current analyzers, there have been attempts to compensate for these errors caused by inexact pipette suction by using sufficiently great liquid volumes of tens to hundreds of micro-liters for minor air bubbles or any last liquid droplet remaining at the pipette end not to have any practical impact in terms of the quantitative result of the tests. However, as a result of this, the operational components of the analyzer, i.e. sample tubes, reagent containers and measurement filter troughs need to be given unnecessarily large dimensions in view of the actual test reaction, and also reagent consumption will be high. For these reasons and for the operational versatility required, current analyzers are typically large apparatuses of the size of a desk approximately, requiring professional staff for use and entailing high costs of investment and operation.